This research deals with the photophysics of photodynamic therapy (PDT) utilizing coherent and noncoherent light and it's tissue transport to PDT cancer treatment sites. Our objectives are to quantitate the processes of scatter, reflection and absorbance in tissue and learn how these principles may be utilized. We have begun to develop procedures for the estimation and delivery of a uniform, efficient photon light dosage so that tumor oblation may occur without damage to normal tissue. We have studied the red region and the visible band from both laser and incoherent sources, coupling laser beams to fiberoptics for instillation, and using beam expanders and incoherent sources for external light delivery. We have compiled transmittance and spectral data on many mammalian tissues at PDT wavelengths, and for the 400 to 1100 nm band have established penetration depths across this region for several tissues. We are extending this research. Study has been carried out in tissue, on simulators, and with tissue phantoms. A series of mammalian tissues is being studied across species boundaries. Species similarities and variations have been established. This cross-species investigation continues and will include human specimens during the later research phase. The ultimate goal is establishment of a photon dosage prediction system for all tissue, tumor types, for photon energies, and sources. We are developing a method of experimentally determining space irradiance, describing the level and extent of light diffusion through a three dimensional tissue volume. Our experimental results in three dimensions, to date, show a basic exponential form. This finding, which supports some of the proposed theoretical models, developed by ourselves and others, is the result of the first systematic series of measurements in 3-D tissue volumes. Additionally, work will be carried out concurrently on a theoretical base for the prediction of transport of light through tissue. Applications of the diffision and Kubelka-Monk equations are being made to interpret our experimental data. We shall expand our determinations of tissue refraction for selected wavelengths, and of scattering and absorption coefficients. We have developed several computer programs to aid in the experimental and theoretical work and they are now in use. Basic data generated by this study will be used to develop a light dosage planning system for PDT clinical use.